380 EXTINCT AND VANISHING MAMMALS 



seems to be known of the species, but presumably it still is to 

 be found on its island home. 



INDEFATIGABLE RICE RAT 

 NESORYZOMYS INDEFESSUS (Thomas) 



Oryzomys indefessus Thomas, Ann. Mag. Nat. Hist., ser. 7, vol. 4, p. 280, 1899 ("Inde- 

 fatigable Island," Galapagos group). 

 FIGS.: Orr, 1938, pi. 25, figs. 3, 3a (skull). 



This and the three other remaining rodents of these islands 

 are placed in a somewhat aberrant genus, Nesoryzomys, which, 

 though thus far considered endemic, may nevertheless eventu- 

 ally prove to be represented on the mainland of South America, 

 as Osgood (1929) has remarked. Compared with typical 

 Oryzomys, the frontal bones are much narrower, with rounded 

 orbital edges; the snout is more elongate, the nasals narrower 

 and less convex in profile, and the tooth rows are shorter. 

 Externally the fur and the tail are shorter. The present species 

 is dull mouse gray above, heavily lined with black, and with a 

 slight tinge of fawn on the posterior back; below, the hairs are 

 slaty at the base, tipped with white. The tail is about as long 

 as head and body, well haired, black above and white below. 

 An average specimen measures: Total length, 269 mm.; tail, 

 108; hind foot, 29; ear, 22. Skull length, 35.3. 



This species was described from a specimen taken on Inde- 

 fatigable Island by the Rothschild Expedition. Later, in 

 1898-99, Heller found it abundant on the same island, as well 

 as on South Seymour Island, and secured a series of specimens. 

 He did not find it on the adjacent North Seymour Island. 

 He writes (1904) that it "seems to be more nocturnal in habits 

 than Oryzomys. It inhabits burrows or rock crevices beneath 

 bushes." Nothing further is known of its habits. Although 

 at present believed to be still common, it is probable that if 

 Old World rats and mice or house cats (the latter recently 

 introduced) should become established on these islands, as 

 they have on some others of the group, this native rat would 

 be in jeopardy. 



NARBOROUGH RICE RAT 

 NESORYZOMYS NARBOROUGHI Heller 



Nesoryzomys narboroughi Heller, Proc. California Acad. Sci., ser. 3, zool., vol. 3, p. 242, 



Aug. 31, 1904 ("Narborough Island," Galapagos group). 

 FIGS.: Orr, 1938, pi. 25, figs. 2, 2a (skull). 



